FIG. 30 shows a conventional example of an air-cushion belt conveyor used in various industrial fields.
In the air-cushion belt conveyor (hereinafter simply referred to as a belt conveyor) 201, an endless belt (hereinafter simply referred to as a belt) 202 is installed around a pair of end pulleys 203, 204 provided at both ends of the belt conveyor 201 with their axes horizontally placed. The pulleys 203, 204 rotate toward a direction indicated by an arrow H in the Figure, thereby causing the belt 202 to circulate along a direction indicated by an arrow F. Troughs 205 (see FIG. 31) of circular-arc cross-section are provided close to the underside of a belt portion located on the upper side, i.e., forward (also referred to as outward) belt.
The belt 202 is generally comprised of a core body made of cotton, vinylon, nylon, polyester, steel code and the like, and rubber covering the core body.
Between the end pulley 203 on a trough entrance side and an entrance 205a of the trough 205, upper-stage support roller trains 206 such as trough rollers, impact rollers, or the like for supporting the forward belt 202 from below, are arranged. Each of the upper-stage support roller trains 206 forms a trough angle. Specifically, as shown in FIG. 31(a), the upper support roller train 206 is configured such that a plurality of rollers 206a are arranged in the shape of circular-arc to cause the belt 202 to be curved in the width direction as shown in FIG. 31(a) to thereby allow curvature of cross-section of the belt 202 to conform to that of the troughs 205 (see FIG. 31(b)). Meanwhile, below a belt portion under the troughs 205, i.e., a return (also referred to as homeward) belt, lower-stage support roller trains 207 comprised of flat rollers or the like for supporting the return belt portion to be flat are provided. In some cases, the lower-stage support roller trains 207 on the return side are also configured such that a plurality of rollers are arranged in the shape of circular-arc similarly to the forward trains. The upper-stage support roller trains 206 and the lower-stage support roller trains 207 are arranged as being spaced along the longitudinal direction of the belt 202.
As shown in a plan view of FIG. 32(a), the support rollers 206a in the respective upper-stage support roller trains 206 are arranged in such a manner that gaps G between the rollers are arranged on straight lines as seen from the longitudinal direction of the belt. The support rollers 207a in the lower-stage support roller trains 207 are arranged in the same manner, although this is not shown.
Therefore, the belt 202 is deformed by upward bending at positions corresponding to the gaps G between rollers along the longitudinal direction of the belt (see arrows in FIG. 32(b)). The deformation by bending is a characteristic in which once the belt is bent toward one direction, the resistive force to the bending toward the same direction is reduced even after the belt is restored to its original shape after the corresponding bending force is released. On the other hand, the resistive force is increased when the belt is bent toward the opposite direction to initial bending. This characteristic is believed to be attributed to visco-elasticity of rubber as a material of the belt 202.
Specifically, as shown in FIG. 32(b), the belt portion 202 on both sides around the gap G between adjacent rollers (represented by reference numeral 206a) as a center axis is upwardly bent. After this bending is released and a belt shape is thereby restored, the belt portion tends to be easily bent upwardly.
As a result, when this portion of the belt 202 moves up onto the trough 205, and is pushed up by compressed air, as shown in FIG. 32(c), the cross-section of the belt 202 in the width direction have corners C rather than smooth circular-arc (for easier understanding, the shape is exaggerated in the Figure). In order to prevent the corners C from making contact with the trough 205, it is necessary to increase an air pressure to thereby increase a floating force. This might cause an increase in the amount of air escaping from the side portions of the belt 202.
Meanwhile, between the end pulley 203 on the trough entrance side and the entrance 205a of the troughs 205, a shoot 208 is provided for dropping the products onto the belt 202. As shown in FIG. 31(a), the width of a lower end opening 208a of the shoot 208, i.e., the dimension of the lower end opening 208a in the belt width direction is set slightly smaller than the width of the belt 202. This is because the excess reduction of the width might cause the shoot 208 to get clogged with the products. Skirts 209 are provided on both sides of the belt 202 in the width direction in the vicinity of where the shoot 208 is provided, to prevent dropping of the products from the belt. The support roller train 206 provided under the belt portion at a position corresponding to the position of the shoot 208 functions as impact rollers 206 for receiving drop load of the dropped products. The impact rollers 206 are, as described above, configured such that, the plurality of rollers 206a are arranged in the shape of circular-arc to cause the belt 202 to be curved in the width direction to thereby allow curvature of cross-section of the belt 202 to conform to that of the troughs 205 (see FIG. 31(b)). A belt portion between the both end pulleys 203, 204 is surrounded by a duct 210.
As shown in FIG. 31(b), an air-supply hole 211 is formed at the bottom of the trough 205. For the purpose of floating the belt 202 above the trough 205, an air-supply device 212 is provided for injecting compressed air into between the belt 202 and the trough 205 through the air-supply hole 211.
It is preferable that, in the belt conveyor, in particular in the air-cushion belt conveyor, the products are evenly loaded in right and left direction with respect to a center portion on the belt portion in the width direction. This is because if the products are unevenly loaded in the width direction of the belt, the belt is likely to snake because of directional imbalance between the floating force of air and the gravity of the products above the trough. However, in the belt conveyor 201 provided with the shoot 208 having a large opening width, the products are unevenly arranged on the belt 202 depending on the state of the products dropping through the inside of the shoot 208, thereby causing the belt 202 to snake.
Accordingly, as a solution to this problem, belt conveyors have been proposed as disclosed in Japanese Laid-Open Patent Application Publication Nos. 7-125826, 9-169423. The belt conveyor comprises a sensor for detecting snaking of the belt, and a mechanism for pivoting a shoot or a damper at a lower end of the shoot in the width direction of the belt. With such a configuration, a detection signal of the snaking detection sensor is fed back to the shoot (damper) pivoting mechanism to change the positions of the products being loaded toward the direction for canceling the snaking. However, such a conveyor is complex in mechanism, and the number of parts is greatly increased.
In general, in the above-mentioned conveyor, when the belt 202 is curved by the upper support roller trains 206 to cause the cross-section of the belt 202 to conform in curvature to that of the trough 205; the belt is thereafter restored to a flat shape. As a result, when the belt 202 moves up onto the trough 205, both side portions of the belt 202 are brought into contact with the trough 205, and a space for compressed air for air-cushion is ensured between the belt 202 and the trough 205.
However, in the case where the belt 202 is moving while its both side portions are in sliding contact with the trough 205, friction resistance generated between the side portions of the belt and the trough becomes large and therefore is not negligible. As a result, it is necessary to select a driver which outputs a high power for rotatably driving the pulleys 203, 204. Further, the friction between the side portions of the belt 202 and the trough makes the life of the belt 202 shorter.
The trough of the air-cushion belt conveyor is provided with an extension/contraction allowance in the total length of the conveyor for absorbing thermal expansion, manufacturing error, installation error, etc, which are associated with the troughs.
FIGS. 33(a), 33(b), and 33(c) are a plan view, a longitudinal sectional view, and a side cross-sectional view, respectively, showing a general connecting method of the troughs. The air-cushion belt conveyor is constituted such that air for air-cushion is supplied between the arc-shaped troughs 205 and the inwardly provided belt 202 from an air-supply chamber 213 under the trough 205 through the air-supply hole 211, thereby causing the belt 202 to float and move. When the troughs 205 form a long carrying path, a gap 214 is provided at the connecting portion between the troughs 205 as an extension/contraction allowance. A backing plate (guide plate) 217 is provided between adjacent troughs 205, for covering the gap 214, and a small air passage (groove) 218 is formed between the gap 214 between the troughs 205 and the surface of the backing plate 217.
For this reason, the air for air-cushion flowing between the belt 202 and the troughs 205 flows outward in the width direction of the troughs 205 along the air passage (groove) 218 and leaks outside at the side portions. As a result, the belt 202 is floating unstably, which increases a moving resistance. It is therefore necessary to enhance a capability of a blower and thereby increase a supply amount of the air for air-cushion.
Besides, when the troughs 205 are extended/contracted by heat or the like, and in this state, the troughs 205 slide, this causes change in the gap 214 between the trough 205, i.e., air passage (groove) 218, and hence change in leakage amount of the air for air-cushion leaking outside through the air passage (groove) 218. This leads to unstable flotation of the belt 202, which is brought into contact with the troughs 205, thereby resulting in an increase in a moving resistance.
Japanese Laid-Open Patent Application Publication No. Hei. 10-316244 discloses a technique in which, for the purpose of simplifying a connecting work of the troughs, a connecting guide member is protruded by a predetermined amount from a rear end face of one of the troughs, the other trough is positioned on the upper side of a connecting guide member, and bond is filled between end faces of these troughs. This prior art is disadvantageous in that the sliding of the trough extended/contracted due to heat is not permitted, although there are no grooves through which the air for air-cushion escapes.
The products adhere to the belt 202 and such residues are carried along with movement of the belt 202. Then, they drop, fly, or adhere around a return belt moving path, thereby causing contamination, corrosion, deposition, or change in moving resistance.
Accordingly, there has been conventionally proposed a device for removing residues on the belt on the return side. The residue removing means includes scraping by cleaners, or cutwater rollers (the roller adapted to press against the belt).
Publication of Unexamined Patent Application Publication No. Hei. 7-20767 discloses a blade constituting a scraper, which is mounted to extend in the width direction of the belt and to be adjustably positioned by rotation around an axis extending in the width direction of the belt. The blade is curved as having a distance from the axis increasing from both sides of the belt toward its center portion as seen from the width direction of the belt. When the blade rotates around the axis and its center portion in the width direction rises up with respect to the belt, this becomes an arch-shaped scraping portion for the belt. In accordance with this, even when the belt is deformed by the troughs in the shape of arch, i.e., deformed by bending, the scraping portion can be made into contact with the belt surface without gap between the scraping portion of the belt and the belt surface. As a result, the residues on the belt surface can be suitably scraped.
Japanese Laid-Open Patent Application Publication No. Hei. 6-271045 discloses that first to third processing rollers are rotatably provided in the vicinity of a terminal end portion of the belt conveyor, for guiding the belt inverted at the terminal end portion to snake. In accordance with this, while the belt inverted at the terminal end portion of the belt conveyor snakes through the first to third processing roller, the residues are pressed between the belt and the first processing roller into dehydrated and layered pieces, which are bent and cracked by the processing rollers, and the resulting layered broken pieces can be scraped and removed from the belt surface by bringing the third processing roller into contact with the belt.
Meanwhile, the belt is deformed by bending by the support roller trains. This is because, the cross-section of the belt is supported to be arch-shaped by the guide rollers having the trough angles as described above, for stably loading the products on the forward belt moving outward with the products loaded thereon.
Since each of the above means is adapted to remove the residues while keeping the cross-section of the belt in the shape of a straight line, the residue removing capability is high at the center portion of the belt but is low at the belt side portions due to the deformation by bending of the belt and reduction of the pressing force. In general, since the residues are less at the belt side portions than at the center portion, attention has been hardly focused on removal of the residues at the belt side portions. Under the circumstances, effective removing means has not been proposed.